Lactic acid, its salts and esters have long been used as food additive and in various chemical and pharmaceutical applications. More recently, lactic acid has been used in the making of biodegradable polymers both as a replacement for present plastic materials as well as various new uses where biodegradability is needed or desired such as for medical implants, solvable sutures and controlled release drugs. The production of lactic acid is commonly carried out by fermentation by means of a micro-organism such as bacteria, yeasts and fungi. The fermentation medium consists of a carbohydrate substrate together with suitable mineral and proteinaceous nutrients. A commonly used fermentation substrate is white sugar. Sugar is the most important contributor to the manufacturing cost price of lactic acid. Major reductions in the manufacturing cost price of lactic acid can therefore be accomplished if a less expensive carbohydrate source can be used than white sugar. To this end several research groups tried to ferment cheaper byproducts and intermediates of a sugar production plant to lactic acid. However, while the fermentation of these crude sugar sources to ethanol can be done readily, problems are encountered when trying to use these substrates on industrial scale for the fermentation to lactic acid. These problems lie in the field of fermentability, storage—stability, sensitivity to infections, the purification of the product of fermentation (i.e. the downstream processing) etcetera.
Examples of prior art wherein the fermentation of sugar beet juice to ethanol is described are Raw thick juice: manufacture, storage and utilisation as feedstock in biotechnological industry, G. Marke, P. V. Schmidt, R. Rieck, B. Senge, B. Steiner, Zuckerindustrie (1992), 117 (12), 984-90, The manufacture of alcohol from sugar beets, K. Antal, Zeitschrift fuer Spiritusindustrie (1911) 34, 239-40, 252-3 and Combined production of ethanol and white sugar, K. Austmeyer, H Roever, H. Zuckerindustrie (1988) 113 (9), 765-72.
The literature on fermentation of sugar beet juice to lactic acid on industrial scale is not so abundant.
For instance, in The industrial preparation of lactic acid from sugar beets, A. Bonelli, G. Gulinelli, Ind. Chim. Met. (1918), 5 121-4, the fermentation of raw sugar beet juice to lactic acid is described. This raw sugar beet juice only has a concentration of about 16 wt % sugar. First of all, as indicated in the publication this carbohydrate source is very sensitive to infections and often already infected to start with. This is confirmed in for instance, F. Hollaus et Al: “Experimental studies on bacterial degradation in sugar of sugar in raw juice and preliming juice.” Sucrerie beige, vol 99, No 5, (1980), p. 183. With sugar beet factories running in campaigns and only active 3-4 months a year, it is clear that this provides storage problems. Secondly, with a concentration of only 16% the transport and storage costs will render this process relatively expensive. These factors make raw sugar beet juice unfit as a substrate for fermentation to lactic acid on an industrial scale.
In Production of lactic acid from sugar beet and cases of inactivation of lactic acid fermentation, I. P. Zakharov, M. F. Federova, Mikrobiologiya (1946), 15 (No. 1), 57-66, also the fermentation of raw sugar beet juice is described. Zakharov reports that the heating or sterilization of the sugar beet juice has a detrimental effect on the fermentation. The beet syrup, prepared by evaporation of beet juice to a sugar content of 51% was diluted and fermentation was tried: virtually no fermentation took place both with and without chalk (probably calcium hydroxide is meant here) addition. Zakharov concluded that a medium of such syrup proved unsuitable for the fermentation to lactic acid.